Polyamides have excellent mechanical strength. Of these polyamides, an aromatic polyamide is excellent in heat resistance and therefore it is expected to be developed into electronic material applications. When an NH group of an amide bond and a hydroxyl group, a thiol group or a carboxyl group are bonded to the aromatic ring at the ortho-position in the aromatic polyamide, heating causes intramolecular cyclization accompanied with elimination of water, resulting in conversion into a heterocyclic polymer having further excellent heat resistance. Recently, a positive photosensitive resin having excellent heat resistance has flourishingly developed utilizing such characteristics (see, for example, Patent Documents 1 to 3).
In use for the field of microelectronics, use of a chemical containing metal ions may exert an adverse influence on the electrical function of the device. Therefore, it is necessary that the polymer used in such applications is soluble in a metal ion-free developer.
As the method for producing an alkali-soluble polyamide, a method of reacting a dicarboxy dichloride with a proper diamine having an alkali-soluble group is known. A soluble base such as pyridine is usually added so as to trap hydrogen chloride generated during the reaction (see, for example, Patent Documents 4 to 5). Although a polymer soluble in a metal ion-free aqueous alkaline developer can be produced, chlorine ions are remained in the polymer. Since chlorine ions may cause corrosion to drastically damage the function of the device, chlorine ions must be removed by purification of the polymer using an ion exchanger.
As the method for producing a chlorine-free alkali-soluble polyamide, for example, there has been proposed a method of reacting a diamino compound having an alkali-soluble group with dicarboxylic acid in the presence of carbodiimide (see, for example, Patent Document 6). However, in the case of this reaction, a urea group remained by the rearrangement reaction of urea may exert an adverse influence on the quality of a heat-resistant layer to be finally formed. Also, the polymer produced by this method is not sufficiently soluble in the metal ion-free aqueous alkaline developer.
In order to solve these problems, a method for producing an alkali-soluble polyamide using various active dicarboxylic acid esters has been proposed (see, for example, Patent Documents 7 to 8). These active dicarboxylic acid esters enable removal of impurities that cause erratic behavior of the device, and suppression of deterioration of alkaline solubility. However, reprecipitation in a water/alcohol mixed solvent and washing with an alcohol after the polymerization were required so as to remove a by-product eliminated from active ester.
As the method for producing a high molecular weight aromatic polyamide, there has been proposed a diimidazole polycondensation reaction between diimidazolide of an aromatic dicarboxylic acid and an aromatic diamine (see, for example, Non-Patent Document 1). However, it was necessary to add a strong acid catalyst such as hydrochloric acid or Lewis acid because of an insufficient reaction rate in the absence of a catalyst.
[Patent Document 1] Japanese Unexamined Patent Publication (Kokai) No. 2005-215436
[Patent Document 2] Japanese Unexamined Patent Publication (Kokai) No. 2006-162791
[Patent Document 3] Japanese Unexamined Patent Publication (Kokai) No. 2007-193322
[Patent Document 4] EP 0 264 678 specification
[Patent Document 5] EP 0 291 779 specification
[Patent Document 6] EP 0 158 726 specification
[Patent Document 7] Japanese Patent No. 3,167,628 specification
[Patent Document 8] Japanese Patent No. 3,311,600 specification
[Non-Patent Document 1] “Journal of the Chemical Society of Japan, Industrial Chemistry Section”, 1969, Vol. 72, No. 7, pp. 187-191